1. Field of the Invention
The present invention relates to an image recording apparatus using a plurality of light modulator elements for recording an image on a recording medium.
2. Description of the Background Art
Developed has been a diffraction grating type light modulator element which is capable of changing the depth of grating by alternately forming fixed ribbons and moving ribbons on a substrate with a semiconductor device manufacturing technique and sagging the moving ribbons relatively to the fixed ribbons. It is proposed that such a diffraction grating as above, in which the intensities of a normally reflected light beam and diffracted light beams are changed by changing the depth of grooves, should be used for an image recording apparatus in techniques such as CTP (Computer to Plate) as a switching element of light.
For example, a plurality of diffraction grating type light modulator elements provided in the image recording apparatus are irradiated with light, and then reflected light beams (zeroth order diffracted light beams) from light modulator elements in a state where the fixed ribbons and the moving ribbons are positioned at the same height from a base surface are guided to the recording medium and non-zeroth order diffracted light beams (mainly first order diffracted light beams) from light modulator elements in a state where the moving ribbons are sagged are blocked, to achieve an image recording on the recording medium.
In such a diffraction grating type light modulator element, however, since the driving voltage supplied for the moving ribbons and the amount of sag of the moving ribbons are not in proportion to each other, even if a curve indicating a change in driving voltage at the time when the light modulator element is changed from an ON state (a state where a signal beam is guided from the light modulator element to the recording medium) to an OFF state (a state where no light is guided from the light modulator element to the recording medium) is made equivalent (symmetrical) to a curve indicating a change in driving voltage at the time when the light modulator element is changed from the OFF state to the ON state, changes in intensity of light outputted from the light modulator element in both the cases do not become equivalent (symmetrical) to each other.
Specifically, when the light modulator element is changed from a state where the change in sag of the moving ribbons is large with respect to the change in driving voltage to a state where the change in sag is small, it is hard for the moving ribbons to follow the driving voltage since a large initial acceleration is given to the moving ribbons and this results in excessively quick moving of the moving ribbons and oscillation thereof. As a result, even if the light modulator elements are changed periodically between the ON state and the OFF state, it is hard to write appropriate dots on the recording medium which travels at constant speed relatively to the light modulator elements.
In a case where an image is recorded on the recording medium by using various light modulator elements (including a light modulator element which emits a light such as a laser), not limited to the diffraction grating type one, when the respective areas on the recording medium which are irradiated with lights by a plurality of light modulator elements are different in size, even if the lights are emitted from the light modulator elements with the same intensity at the same timing, disadvantageously, the same drawing can not be performed on the recording medium.
It is an object of the present invention to achieve an appropriate image recording by using a plurality of light modulator elements.
The present invention is intended for an image recording apparatus for recording an image on a recording medium by exposure.
According to a preferred embodiment of the present invention, the image recording apparatus comprises a light modulator having a plurality of light modulator elements, a holding part for holding a recording medium on which an image is recorded with signal beams from the plurality of light modulator elements, a transfer mechanism for transferring the holding part relatively to the light modulator, a state transition detection circuit for detecting whether or not there is a transition between a state of emitting a signal beam and a state of emitting no signal beam on each of the plurality of light modulator elements, and a control circuit for shifting a transition timing of each element on which the transition is detected in accordance with a detection result of the state transition detection circuit.
In the image recording apparatus of the present invention, it is possible to record an appropriate image while suppressing at least any of effects of the state transition characteristics of each light modulator element, the width of each irradiation area in a scan direction, a positional shift of each irradiation area, the photosensitive characteristics of the recording medium and the like by shifting a transition timing of each light modulator element.
According to one aspect of the present invention, the image recording apparatus further comprises a beam sensor and shift times are calculated on the basis of widths of irradiation areas irradiated by the light modulator elements in the scan direction or positional shifts of the irradiation areas in the scan direction, respectively.
Preferably, each of the plurality of light modulator elements is a light modulator element of diffraction grating type in which strip-like fixed reflection surfaces and strip-like moving reflection surfaces are alternately arranged.
According to another aspect of the present invention, the state transition detection circuit detects a state transition of each of the light modulator elements in a series of points of time, and the control circuit applies an auxiliary driving voltage which is different from a normal driving voltage to each light modulator element on which a specified state transition is detected.
It is also possible to record a fine image pattern with high precision by changing the driving voltage as well as the shift time in transition timing.
Further preferably, the control circuit shifts a driving timing of each light modulator element on which a specified state transition is detected by an auxiliary shift time which is different from a normal shift time.
The present invention is also intended for an image recording method of recording an image on a recording medium with signal beams from a light modulator having a plurality of light modulator elements.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.